Question: Find the missing fraction. $\dfrac{2}{5} + $
Let's look at the multiples of each denominator and see which multiples they have in common. Denominator Multiples ${5}$ $5, \underline{{10}}, 15$ ${10}$ $\underline{{10}}, 20, 30$ The least common multiple is ${10}$. Let's use multiplication to make ${\dfrac{2}{5}}$ have a denominator of $10$. ${\dfrac{2}{5}}=\dfrac{{2} \times 2}{{5} \times 2} = {\dfrac{4}{10}}$ So, ${\dfrac4{10}} + \boxed{\phantom{\dfrac14}} = {\dfrac{7}{10}}$ $\dfrac{4}{10}$ $\boxed{\phantom{\dfrac{3}{10}}}$ ${\dfrac{7}{10}}$ $+$ ${\dfrac4{10}} + \boxed{{\dfrac3{10}}} = {\dfrac{7}{10}}$ $\dfrac{4}{10}$ $\dfrac{3}{10}$ ${\dfrac{7}{10}}$ $+$ ${\dfrac4{10}} + \boxed{{\dfrac3{10}}} = {\dfrac{7}{10}}$